Transportation networks may include multiple general parallel routes or sub-routes (e.g., railroad tracks, highway lanes, or the like) over which vehicles may travel. Further, vehicles may be able to switch from traveling on a given one of the parallel sub-routes to a different of the parallel sub-routes. It may be desirable or necessary for a control system to have knowledge of the particular sub-route upon which a vehicle is traveling.
For example, positive or automatic control systems may be employed in transportation networks. Such control systems may require knowledge of a particular track or sub-route on which a vehicle is traveling to properly control the vehicle based on a status of a switch or crossing, the presence of other vehicles on a given track or sub-route, any dangers or impediments to travel on a given track or sub-route, or the like. As one example, a Positive Train Control (PTC) system may be understood as a system for monitoring and controlling the movement of a rail vehicle such as a train to provide increased safety. A train, for example, may receive information about where the train is allowed to safely travel, with onboard equipment configured to apply the information to control the train or enforce control activities in accordance with the information. For example, a PTC system may force a train to slow or stop based on the condition of a signal, switch, crossing, or the like that the train is approaching.
However, PTC systems may have difficulty in accurately determining or establishing which track a train is on. For example, the centers of adjacent train tracks may be as close as about 14 feet. Global positioning system (GPS), even with corrections, may not provide sufficient accuracy to safely or conclusively determine alone which track a train is on. Location determination systems that may be able to provide sufficient accuracy may require additional positioning devices to augment GPS and may be very expensive or cost prohibitive. Thus, PTC systems may rely on an operator of a train to initially enter a particular track on which the train is located, with the train relying on knowledge of the position of track switches to determine which track the train is on as the train travels. However, the initial manual entry of track location is subject to error and can compromise the safety benefit provided by a PTC system. Further, track identification information may need to be re-entered each time a vehicle cuts into a PTC territory from a territory not covered by a PTC system. Such re-entering may require the vehicle to be located within a portion of a route that has only one track, may require a stop, may require operator input, or the like.
Cab signal systems may be employed in an attempt to identify which track a train is traveling upon. In such systems, a transmitter is utilized to send a signal down the rails of the track, with the signal received by an onboard receiver through magnetic induction into an antenna mounted on the front of the train. Each track could have a unique signal identifying which track is being traveled upon. However, in such systems, a large amount of energy may be required to transmit through the rail for reliable signal to noise ratios for the signal received by the train. Further still, insulated joints are required in each track to electrically isolate the rails from each other and control the flow of current. Thus, such systems may be very expensive or cost prohibitive, and may also compromise the structural integrity of the track.
Radiofrequency identification (RFID) tags may also be employed in an attempt to identify which track a train is traveling upon. In such systems, a passive tag may be placed between rails of each track and pre-programmed with information identifying the particular tracks. An active reader onboard the train may interrogate the tag as the train passes over the tag. However, such RFID tags are exposed to the elements as well as vandalism, reducing reliability as well as increasing maintenance and replacement time and costs. Further, such tags may require batteries which further increase maintenance time and costs.